High-performance requirements to plastics have more increased recently, and thus a lot of polymers with various novel performances have been developed and marketed. Among these, liquid crystalline resins such as optically anisotropic liquid crystalline polyesters characterized by a parallel arrangement of molecular chains have become of major interest in view of excellent moldability and mechanical properties and demands have increases in injection molding applications mainly for electric/electronic components.
However, when the liquid crystalline resins are used alone and in combination with other thermoplastic resins, very large anisotropy exceeds the limitation of use or design of moldings and the use may be limited.
Therefore, for the purpose of reducing anisotropy, it is studied to introduce branching by blending a liquid crystalline polyester with a tri- or tetrafunctional compound by copolymerization or kneading (refer to patent Japanese Unexamined Patent Publication (Kokai) No. 58-104924 (page 1 to 5); and Japanese Examined Patent Publication (Kokoku) No. 5-38007 (pages 1 and 2)).
Japanese Unexamined Patent Publication (Kokai) No. 58-104924 (page 1 to 5) describes that a mechanical strength in a transverse direction of a liquid crystalline resin is improved by introducing a small amount of a branched structure, and Japanese Examined Patent Publication (Kokoku) No. 5-38007 (pages 1 and 2) describes that flow anisotropy of a liquid crystalline resin is improved by introducing a small amount of a branched structure. However, when crosslinking points are introduced into the liquid crystalline resin, since an ordered structure of the liquid crystalline resin is broken, it cannot be said that the effect has a sufficient balance.
It is also studied to introduce a similar branched structure so as to attain balance between weld strength and moldability (refer to Japanese Unexamined Patent Publication (Kokai) No. 3-275715 (page 1); and Japanese Unexamined Patent Publication (Kokai) No. 6-340797 (page 1).
In Japanese Unexamined Patent Publication (Kokai) No. 3-275715 (page 1), it is studied to achieve high polymerization degree by copolymerizing a liquid crystalline resin with a tri- or tetrafunctional structural unit. Although mechanical properties and weld strength are surely improved, melt viscosity increases when compared with a non-crosslinked polymer having an identical molecular weight, and fluidity is not improved.
In Japanese Unexamined Patent Publication (Kokai) No. 6-340797 (page), a polyester oligomer having a tetra-branched structure is blended with a liquid crystalline resin, and thus mold releasability is improved and also a good balance between mechanical properties is achieved. However, the polyester oligomer having a branched structure and a liquid crystalline resin are not positively reacted and performances deteriorate when an additive amount increases.
It is also studied to develop polyamide having a hyperbranched-structure, and to improve fluidity by blending the polyamide with a thermoplastic resin (refer to Published Japanese Translation No. 2005-513186 of the PCT Application (page 1); and Japanese Unexamined Patent Publication (Kokai) No. 2000-264965 (page 1)).
In Published Japanese Translation No. 2005-513186 of the PCT Application (page 1); and Japanese Unexamined Patent Publication (Kokai) No. 2000-264965 (page 1), a hyperbranched-polymer having a heteroatom as a branching point is studied. In case of having a heterobranching point, sufficient performances cannot be obtained since thermostability is not sufficient.
Japanese Unexamined Patent Publication (Kokai) No. 5-214083 (page 1 to 2) discloses synthesis of a heterobranched polymer by polymerizing only a branched structure.